src/transform/emit_vertex_point_size.cc

// Copyright 2020 The Tint Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#include "src/transform/emit_vertex_point_size.h"

#include <utility>

#include "src/ast/assignment_statement.h"
#include "src/program_builder.h"

namespace tint {
namespace transform {
namespace {

const char kPointSizeVar[] = "tint_pointsize";

}  // namespace

EmitVertexPointSize::EmitVertexPointSize() = default;
EmitVertexPointSize::~EmitVertexPointSize() = default;

Transform::Output EmitVertexPointSize::Run(const Program* in, const DataMap&) {
  if (!in->AST().Functions().HasStage(ast::PipelineStage::kVertex)) {
    // If the module doesn't have any vertex stages, then there's nothing to do.
    return Output(Program(in->Clone()));
  }

  ProgramBuilder out;
  auto* f32 = out.create<type::F32>();

  // Declare the pointsize builtin output variable.
  auto* pointsize_var = out.create<ast::Variable>(
      Source{},                               // source
      out.Symbols().Register(kPointSizeVar),  // symbol
      ast::StorageClass::kOutput,             // storage_class
      f32,                                    // type
      false,                                  // is_const
      nullptr,                                // constructor
      ast::DecorationList{
          out.create<ast::BuiltinDecoration>(Source{},
                                             ast::Builtin::kPointSize),
      });
  out.AST().AddGlobalVariable(pointsize_var);

  // Add the pointsize assignment statement to the front of all vertex stages.
  CloneContext ctx(&out, in);
  ctx.ReplaceAll([&](ast::Function* func) -> ast::Function* {
    if (func->pipeline_stage() != ast::PipelineStage::kVertex) {
      return nullptr;  // Just clone func
    }

    // Build the AST expression & statement for assigning pointsize one.
    auto* one = out.create<ast::ScalarConstructorExpression>(
        Source{}, out.create<ast::FloatLiteral>(Source{}, f32, 1.0f));
    auto* pointsize_ident = out.create<ast::IdentifierExpression>(
        Source{}, out.Symbols().Register(kPointSizeVar));
    auto* pointsize_assign =
        out.create<ast::AssignmentStatement>(Source{}, pointsize_ident, one);

    return CloneWithStatementsAtStart(&ctx, func, {pointsize_assign});
  });
  ctx.Clone();

  return Output(Program(std::move(out)));
}

}  // namespace transform
}  // namespace tint